What Does AC Stand For?

AC stands for two everyday things

More letter pairs you meet daily sit on our famous acronyms list.

Air conditioning: the AC at home and in the car

An air conditioner moves heat from inside a room to the outside, which cools the air and also pulls out moisture. That is why a room with the AC on feels less sticky. In a house, the AC is often part of a central system covered by HVAC, which covers heating, ventilation and air conditioning. Window units and wall units are sized by cooling power, often listed in BTU.

In a car, the AC button is often marked with a snowflake. Pressing it turns on the compressor that chills the air. Some drivers also run it in winter for a few minutes, because the dry air helps clear a foggy windshield.

What does AC stand for in electricity?

In electricity, AC stands for alternating current. The current flows one way, then reverses, over and over, many times each second. Power plants and the grid use AC because its voltage is easy to raise for long distance lines and lower again for homes.

• In the United States, standard household outlets supply about 120 volts AC at 60 hertz, meaning 60 full back and forth cycles each second.
• Many other countries use about 230 volts at 50 hertz, which is why travelers need adapters or converters.
• Batteries supply DC, direct current, which flows one way only.

An "AC adapter," the box on many laptop cords, takes AC from the wall and converts it to the low voltage DC the device needs. Lights like LEDs run on DC too, so bulbs include a small converter inside.

AC on prescriptions and in games

On a prescription, the short form is usually written lowercase with periods, a.c., from the Latin ante cibum, "before meals." Its partner is p.c., after meals. If you are unsure what directions mean, ask the pharmacist.

In tabletop role playing games, AC means armor class, a number that shows how hard a character is to hit. A higher AC means better defense. Gamers say it as letters, just like the other meanings.

How to write AC

Capitals with no periods, AC, is the normal form for both main meanings. A/C with a slash is also common for air conditioning, especially in listings and car manuals. Lowercase "ac" in texts is understood but looks casual. Spoken aloud, it opens with "ay," which takes an: "an AC unit," "an AC outlet."

Since you spell it out loud as "A C," it is an initialism. The difference between that and a word style acronym is the subject of our acronym basics guide.

Example sentences and look alikes

• "Can you turn the AC down a little?"
• "The AC in the car quit on the highway."
• "This charger accepts 100 to 240 volts AC."
• "Take the pill a.c. breakfast."

Watch for these near misses. DC is direct current in electronics but also Washington, D.C., the US capital, which has its own DC page. AC/DC on a device means it works with both kinds of current. HVAC is the full heating and cooling system, not only the AC.